In the prior art the thus defined wiper systems are known as pantograph systems or, more commonly, as pantograph arms. U.S. Pat. No. 3,893,204 may be cited as an example of a prior art pantograph arm. In this patent said first element is represented by the reference numeral 20 and is, on one side, attached to the actuating arm by a first rivet and, on the other side, attached to the control arm by a second rivet. Said element 20 may rotate or swivel about the axes formed by said two rivets, which rivets are substantially perpendicular to a surface to be wiped.
Concerning the same U.S. patent it is to be noted that the control arm is attached to its driving mechanism in such a way that it may rotate or swivel about two axes which are substantially perpendicular, one with respect to the other, and of which one is substantially perpendicular to the surface to be wiped.
In said U.S. Pat. No. 3,893,204 and in the present invention said first element thus may rotate or swivel with respect to the control arm. Since said first element is moreover attached by conventional means to the superstructure of the wiper blade, the wiper blade may, under the action of the actuating arm, rotate or swivel with respect to the actuating arm about an axis which is substantially perpendicular to the surface to be wiped. This system, i.e. pantograph arms in general, makes it possible to increase the surface to be wiped by the wiper blade.
It is a known fact that the rivet connection between the control arm and said first element is a very unsatisfactory solution. Indeed the rivet and said first element are subject to torsion forces at each oscillating movement of the actuating arm and of the wiper blade, torsion forces which are due to the curvature of the surface to be wiped, i.e. generally the windshield of a motor vehicle. As a consequence said rivet connection is subject to rapid wear and the wipe quality will diminish with time.
In some know pantograph wiper arms the rivet which links the control arm to said first element has been replaced by a balljoint which, apparently, eliminates the above mentioned disadvantage. In fact even a ball-joint is subject to wear and said wear is not negligible if the ball-joint has not been carefully designed, in particular as to the materials used. Thus special materials must be used and the balljoint becomes rather complex and, consequently, relatively expensive.
It is to be noted that the two substantially perpendicular axes by which the control arm of the U.S. Pat. No. 3,893,204 is linked to its driving mechanism have also been replaced in some known pantograph arms by a ball-joint. The remarks made in the preceding paragraph also apply to this ball-joint.